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Gravity on Earth and in Space

Most of us spend our entire lives held close to Earth's surface by the force of gravity. For a few days or weeks, however, orbiting astronauts experience their surroundings completely differently -- as if there were no gravity at all. This collection of images compares the experience of gravity on Earth with that of the astronauts' perceived weightlessness in space.

Gravity exerts a powerful force on all of us, relentlessly pulling us toward Earth's surface. Everything we do -- getting up, standing, running, eating breakfast -- requires effort, and much of the energy we expend goes toward our struggle against gravity. Every moment, we fight against our own weight and against the weight of objects with which we interact.

Given that we are fighting constantly against gravity, wouldn't life without it be grand? The trip to school would literally be just a hop, skip, and a jump, and so many arduous tasks would be almost effortless. Right? Not so fast.

First of all, escaping Earth's gravity is next to impossible. Earth's gravitational pull decreases the further you move away from the planet's surface. Yet, even 320 km (200 mi) into space, the force of Earth's gravity on astronauts and their spacecrafts is still 90 percent of what it is on Earth's surface, so they still weigh 90 percent of their Earthbound weight.

The "weightlessness" that astronauts experience is not the result of an absence of gravity. Instead, it is because they themselves and their spacecrafts are free-falling in gravity. By traveling fast enough horizontally -- about 7.5 km (4.7 miles) per second -- a spacecraft can free-fall in a path that is parallel to Earth's curvature. In other words, the spacecraft falls all the way around the planet, and will continue to do so as long as it maintains its velocity.

Lastly, although some things are easier in weightless conditions, many things are harder. Most importantly, because there is no gravity to hold things down, nothing stays put. Liquids, foods, tools, and even sleeping people, all have to be carefully managed, contained, or strapped down to keep them from drifting away.

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